Walmsley, Timothy GordonCarson, James K.Kloeppel, SteffenChen, QunKong, Lana2026-03-162026-03-162026https://hdl.handle.net/10289/18056The need to decarbonise the industrial sector requires new innovations in high temperature heating. The development of an industrial high temperature heat pump presents not only great emissions reduction potential but also cost saving potential for industrial process heat users. Compared to boilers with efficiencies ranging from 70 to 99%, heat pumps have the ability to leverage renewable electricity to supply heating as a standalone technology (air-source heat pumps), with one unit if electricity being able to supply multiple units of heat (Coefficient of Performance > 1) or integrate with existing boilers to reduce steam demand (air-source or waste heat recovery). This thesis investigates a novel high temperature transcritical CO2 heat pump concept using a case study in milk powder spray drying. A series of cycle architectures were modelled that incorporated internal heat exchangers and cascade arrangements to assess their effect on thermodynamic performance for not only large temperature lifts (>150 °C) but also large temperature glides (>150 °C). A transcritical-transcritical cascade configuration was found to achieve a sink temperature of 200 °C with a COP of 2.22 at moderate discharge pressures (150 bar) compared to what is currently available in the literature (>200 bar). Expansion work recovery, using ejectors and expanders, was further explored to reduce exergy losses, achieving incremental COP gains up to 2.35. However, it was determined that, at this stage, the marginal increases in COP did not overcome the challenges in complexity of integrating an expander or ejector within the system. A comparison of integration options was undertaken that compared the high temperature heat pump integration with fuel switching to electrode or biomass boilers. Hybrid configurations of heat pump and boilers were also assessed at varying utility prices to determine whether an optimum sink temperature existed to minimise the operational cost. With this, a multi-temperature heat pump configuration was found to improve the COP of the heat pump to 2.55 for air heating to 200 °C, which emphasises the importance of temperature profile matching in heat pump design. Operating costs depended on the electricity-to-biomass price ratio and grid emissions intensity. In all cases, electrode boiler conversions had the highest operational cost. Price ratios below 2.75 were favourable for full electrification using a heat pump, while price ratios above 3.67 favoured a full biomass conversion. Between these two price ratios, the optimal hybrid configuration was to supply the air heating up to the temperature level for the fluidised bed (102 °C) using a heat pump and supply the remainder of the heating using a biomass boiler. In comparison to coal, the proposed solutions achieved emissions savings between 55 and 94 %. The wider potential for the high temperature heat pump concept was then estimated, revealing a broader potential for CO2 high temperature heat pumps to supply hundreds of petajoules per year of low-carbon heat across a diverse range of industrial sectors. Due to being able to produce both large temperature glides and large temperature lifts, the CO2 high temperature heat pump was particularly suited for a range of drying processes (further than milk powder spray drying). Potential source and sink streams for the heat pump were identified for each application to estimate possible COPs, which ranged between 2.0 and 3.05 for sink outlet temperatures ranging from 110 to 280 °C. Emissions reduction was shown to be viable for nearly all regions when displacing coal, but requires cleaner electricity grids or higher COPs when displacing natural gas. This thesis contributes an in depth thermodynamic analysis of both a novel high temperature heat pump cycle architecture and a novel application of high temperature heat pumps into the milk powder spray drying process. Additionally, this thesis contributes a cross-sectoral analysis for implementation, collating potential source and sink streams across a variety of applications.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.high temperature heat pumpdecarbonisationspray dryingindustrialco2transcriticalThesis